Approximate multi-level cell memory operations

ABSTRACT

The present technology relaxes the precision (or full data-correctness-guarantees) requirements in memory operations, such as writing or reading, of MLC memories so that an application may write and read a digital data value as an approximate value. Types of MLCs include Flash MLC and MLC Phase Change Memory (PCM) as well as other resistive technologies. Many software applications may not need the accuracy or precision typically used to store and read data values. For example, an application may render an image on a relatively low resolution display and may not need an accurate data value for each pixel. By relaxing the precision or correctness requirements is a memory operation, MLC memories may have increased performance, lifetime, density, and/or energy efficiency.

STATEMENT OF RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/794,740 filed Mar. 11, 2013, entitled, “APPROXIMATE MULTI-LEVEL CELLMEMORY OPERATIONS”, now U.S. Pat. No. 8,861,270 issued Oct. 14, 2014,which is incorporated herein by reference in its entirety.

BACKGROUND

A multi-level cell (MLC) is a memory element capable of storing morethan a single bit of information. MLC memories, such as MLC Flash andMLC Phase Change Memory (PCM), are typically read and written in aniterative manner. PCM is also known as PCME, PRAM, PCRAM, Ovonic UnifiedMemory, Chalcogenide RAM and C-RAM. A programming step is typicallyfollowed by a verify step that verifies the intended value is stored ata particular address.

For example, MLC NAND Flash memory is a MLC Flash technology usingmultiple levels per cell to allow a plurality of bits to be stored usingthe same number of transistors. A typical MLC NAND Flash memory has fourpossible states or values per cell, so the cell can store two bits ofinformation.

MLC PCM memory is a type of non-volatile memory that uses asemiconductor alloy having two states, crystalline and amorphous. Theamount of material in each state changes the resistance of the MLC PCMmemory cell. MLC PCM memory stores each binary bit using the variouselectrical resistances of the semiconductor alloy to program the variouscell values. The phase, and thus resistance value, for each bit vale iscontrolled by applying a voltage to an address so that current maychange the phase and represented value.

SUMMARY

The present technology relaxes the precision (or fulldata-correctness-guarantees) requirements in memory operations, such aswriting or reading, of MLC memories so that an application may write andread a digital data value as an approximate value. Types of MLC memoriesinclude Flash MLC and MLC Phase Change Memory (PCM) as well as otherresistive technologies. Many software applications may not need theaccuracy or precision typically used to store and read data values. Forexample, an application may render an image on a relatively low colorrange display and may not need an accurate data value for each pixel.Other types of data that may tolerate errors include audio data, videodata, machine learning data and/or sensor data. By relaxing theprecision or correctness requirements of a memory operation, MLCmemories may have increased performance (reduced latency), lifetime(increased number or writes or reads before failure), density, and/orenergy efficiency in embodiments.

Typically, each digital value in a MLC memory cell is identified bydetermining whether a sensed analog signal from the MLC cell fallswithin a range of analog values (voltage or charge in Flash MLC andresistance in PCM). When a write circuit attempts to store a digitaldata value in a MLC memory cell, the write circuit attempts to store ananalog value that is very close to a middle point of a range of analogvalues that will correspond to the digital data value or within a targetrange of analog values. Similarly, when a read circuit attempts to reada digital data value in a MLC memory cell, the read circuit attempts toread an analog value that is very close to the middle point of the arange of analog values that will correspond to the digital data value orwithin a target range of analog values.

When writing (or reading) a digital value as an approximate value to aMLC memory, the target range of analog values for a MLC memory isincreased such that the written analog value may fall in a range oflikely values for the MLC memory as well as a range of likely values foran adjacent MLC memory that may lead to a erroneously written value.

In an embodiment, a precision requirement is relaxed by reducing thenumber of iterations used in writing to or reading from a MLC memory.Write operations are made faster by increasing an amount by which thevalue of a cell in the MLC memory is changed on each write iteration. Anamount of energy, or a predetermined analog value, such as apredetermined amount of voltage or current, used to write a digitalvalue in a MLC memory during an iteration may be increased. Theincreased predetermined analog value may be an increased programmingpulse having a large value and/or duration. The increased predeterminedanalog write value reduces the number of iterations needed before asignal representing the digital data value is sensed between a targetrange of values. The signal representing the digital data value mayreach the target range of values with less iteration, but less iterationmay also increase the probability of error. Energy and wear on the MLCmemory may be reduced by widening the range of the predetermined analogvalue used in writing to a MLC memory.

In another embodiment, a signal representing the digital value is notsensed after programming and predetermined numbers of programming pulsesare applied without any sensing or verification step.

In another embodiment, a write operation to a MLC memory is made fasterand with lower energy requirements by reducing the number of iterationsin the write operation such that an analog signal that is used to writeoperation is in the outer distribution of likely analog value used tostore the digital value. In other words, a larger target range of likelyanalog values is used and an analog value (or threshold value) at thebeginning of the target range is used as compared to writing a datavalue as a precision value. Wear on the MLC memory may be reduced inthis embodiment.

In another embodiment, a read operation consumes less energy bycompleting enough iteration to determine a rough vicinity of the analogvalue being read. Similar to a write operation, a larger target range oflikely analog values is used and analog values at the beginning of thelarger target range is used to identify that the read analog valuecorresponds to a particular digital value. Memory latency may beimproved and wear may be improved when a read operation affects wear.Where read operations to one cell may disturb the value of other nearbycells, fewer read iterations may also reduce the probability ofdisturbing the values of nearby cells in an embodiment.

In another embodiment, a probabilistic determination following apre-profiled distribution is made on a read analog signal that mayrepresent one of two values with predetermined distributions. In anembodiment, a particular digital value is provided according to therelative density of each probability distribution.

A method embodiment stores an approximate value in a multi-level memorycell. A first signal is received that represents a first digital valueto be stored in the multi-level cell. A first signal is also receivedthat indicates the first digital value is to be written as theapproximate value in the multi-level cell. At least one programmingpulse is provided to the multi-level cell until a first sensed analogvalue from the multi-level cell is within a first range of values. Asecond signal is received that represents a second digital value to bestored in the multi-level cell. A second signal is received thatindicates the second digital value is to be written as a precise valuein the multi-level cell. At least one programming pulse is provided tothe multi-level cell until a second sensed analog value from themulti-level cell is within a second range of values. The first range ofvalues is wider than a second range of values.

An apparatus embodiment includes at least one controller to provide asignal representing a digital data value and a signal that indicateswhether the digital data value is to be stored as an approximate valueto at least one multi-level cell memory. The multi-level cell memoryincludes an interface to receive the signal representing the digitaldata value and the signal that indicates whether the digital data valueis to be stored as the approximate value. A write circuit provides afirst plurality of predetermined values to the multi-level cell so afirst analog value is stored in the multi-level cell that is in a firstrange of analog values that represents the digital data value when thesignal indicates the data value is to be stored as the approximatevalue. The write circuit provides a second plurality of predeterminedvalues to the multi-level cell so a second analog value is stored in themulti-level cell that represents the digital data value that is in asecond range of analog values when the signal indicates the data is tonot be stored as the approximate value. The first range of analog valuesis wider than the second range of analog values.

In another embodiment, at least one processor readable memory hasprocessor readable instructions encoded thereon. The instructions whenexecuted by the at least one processor performs a method to read anapproximate value and a precise value in an array of multi-level memorycells. The method includes outputting control information to read theprecise value at a first multi-level cell in the array of multi-levelcells. A first digital value corresponding to the precise value isreceived from the first multi-level cell. The first digital value wasobtained by determining whether an analog value from the firstmulti-level cell was between a first range of analog values. Controlinformation to read the approximate value from the first multi-levelcell in the array of multi-level cells is also outputted. A seconddigital value corresponding to the approximate value is received. Thesecond digital value was obtained by determining whether an analogsignal from the first multi-level cell was between a second range ofanalog values. The second range of analog values is wider than the firstrange of analog values.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high-level block diagram of a computing device providingapproximate memory operations to a MLC memory.

FIG. 2 illustrates a high-level block diagram of a MLC memory thatperforms approximate and precise memory operations.

FIG. 3 illustrates a MLC memory having data stored as precise data anddata stored as approximate data.

FIGS. 4A-4B illustrates probabilities and target ranges of analog valuesassociated with storing and reading data as precise data and approximatedata.

FIGS. 5A-C conceptually illustrate writing or reading a data valuestored as approximate data and precise data.

FIGS. 6A-C are flow charts for writing and reading values stored asapproximate data and precise data.

FIG. 7 is an isometric view of an exemplary gaming and media system.

FIG. 8 is an exemplary functional block diagram of components of thegaming and media system.

FIG. 9 illustrates is a block diagram of one embodiment of a networkaccessible computing device.

DETAILED DESCRIPTION

The present technology relaxes the precision requirements in memoryoperations, such as writing or reading, of multi-level cell (MLC) memoryso that an application may store and read a digital data value as anapproximate value. The number of iterations used to write or read from aMLC memory is reduced by expanding the target range of correspondinganalog values that may introduce errors. The amount by which a value ofa MLC memory is changed during a write iteration may also be increasedwhich may also reduce the number of write iterations. A probabilisticdetermination may also be made on a read analog signal that mayrepresent one of a set of values. By relaxing the precision or fulldata-correctness-guarantees of a memory operation, MLC memories may haveincreased performance, lifetime, density, and/or energy efficiency.

Memory operations, such as writing or reading, typically require fulldata-correctness-guarantees (e.g., precision). Memory operations withfull data-correctness-guarantees refer to completing a memory operationsuch that all, or substantially all, bits of the data are correctlywritten or read. However, having memory operations with fulldata-correctness-guarantees, on a full-time basis, is often notpractical for many computing devices. Hardware (e.g., a memory havingmulti-level cells) typically provides strong guarantees for errorcorrection. Software typically relies on the memory device to maintainfull data error-correction guarantees. Such reliance on a memory isdemanding on the associated memory circuits and software. The demand maylead to memory that operate more slowly and consumes more energy.Perhaps worse, the memory may also experience shorter life spans. Forexample, precise MLC Flash memory operations may cause quicker wear outdue to the need for a larger number of write iterations.

Full data-correctness-guarantees (e.g., precision memory operations withan effort to maintain the precision of all bits of data), which areoften required by memory, are not always needed for softwareapplications. Some software applications can tolerate errors in some oftheir data structures, such as, for example, picture data, audio data,video data, sensor data and/or most other data that a user decides tostore. A computing device can process these types of data by storing thedigital data as an approximate value and, at the same time, maintainvirtually no perceptible difference in a user experience during theprocessing of the data. Alternatively, applications may need to storedata precisely (having full data-correctness-guarantees) when an errorin the data would not be desired. A computing device can process thesetypes of data by storing and reading digital data as a precise valuehaving full data-correctness guarantees during memory operations.

FIG. 1 is a high-level block diagram of a computing device 100 thatwrites and reads a digital value as an approximate value to and from aMLC memory 101. In an alternate embodiment, computing device 100 alsowrites and reads a digital data as a precise value to and from a MLCmemory 101. In an embodiment, computing device 100 includes processor102, controller 103, memory 105 and MLC memory 101 that communicate byway of signal path 104 in an embodiment. Application 107 and operatingsystem 106 is stored in memory 105. In an alternate embodiment,application 107 and operating system 106 may be stored in MLC memory101. In an alternate embodiment, the function of controller 103, alongwith approximate memory operations 103 a, may be performed by processor102.

In an embodiment, computing device 100 is included in a video gameconsole and/or media console and illustrated in FIGS. 7 and 8. Inalternate embodiments, computing device 100 may be included in at leasta cell phone, mobile device, embedded system, media console, laptopcomputer, desktop computer, server and/or datacenter. In embodiments,computing device 100 corresponds to computing device 1800 havingparticular hardware components illustrated in FIG. 9 and as describedherein.

In embodiments, computing device 100 is coupled to at least one network.In an embodiment, a network may be the Internet, a Wide Area Network(WAN) or a Local Area Network (LAN), singly or in combination. A networkmay transfer signals by wire or wirelessly, singly or in combination.

Processor 102 may also include a controller, central processing unit(CPU), GPU, digital signal processor (DSP) and/or a field programmablegate array (FPGA).

In embodiments, signal path 104 (as well as other signal paths describedherein) are media that transfers a signal, such as an interconnect,conducting element, contact, pin, region in a semiconductor substrate,wire, metal trace/signal line, or photoelectric conductor, singly or incombination. In an embodiment, multiple signal paths may replace asingle signal path illustrated in the figures and a single signal pathmay replace multiple signal paths illustrated in the figures. Inembodiments, a signal path may include a bus and/or point-to-pointconnection. In an embodiment, a signal path includes control and datasignal lines to carry control and data information as well as timinginformation. In an alternate embodiment, a signal path includes datasignal lines or control signal lines. In still other embodiments, signalpaths are unidirectional (signals that travel in one direction) orbidirectional (signals that travel in two directions) or combinations ofboth unidirectional signal lines and bidirectional signal lines.

In embodiments, processor 102 includes at least one processor thatexecutes (or reads) processor (or machine) readable instructions, suchan operating system 106 and/or application 107. In an embodiment,operating system 106 and application 107 may include one or moresoftware components.

In an embodiment, a software component may include processor/machinereadable instructions when executed by one or more processors performone or more functions. In an embodiment, a software component mayinclude a software program, software object, software function, softwaresubroutine, software method, software instance, script or a codefragment, singly or in combination.

In an embodiment, an application uses the services of an operatingsystem 106 and/or other supporting applications. For example, operatingsystem 106 may include an allocator that is a software component thatallocates and de-allocates portions of memory, such as MLC memory 101,to be used by application 107. In an embodiment, operating system 106keeps track of which portions, or blocks of data, of MLC memory 101include data stored as precise values and which include data stored asapproximate values, as illustrated in FIG. 3.

In an embodiment, application 107 identifies which types of data arewritten and read as approximate data and which types of data are writtenand read as precise data. Application 107 may include language features(such as defined approximate variable structures), analyses, or programlogics to identify and process approximate data values as well asprecise data values in embodiments.

Controller 103 includes approximate memory operations 103 a that is asoftware component that is executed by controller 103 in an embodiment.In an alternate embodiment, controller 103 outputs signals in responseto processor 102 executing approximate memory operations 103 a stored inmemory 105. Signals are output from controller 103 in response tomessages from processor 102 executing approximate memory operations 103a. Controller 103 outputs a signal that represents a digital data valueto be stored as an approximate value and receives a signal thatrepresents digital data stored as an approximate value. The receiveddigital data stored as an approximate value represents an analog signalreceived from a MLC memory cell, of MLC memory 101 that was written asan approximate value in an embodiment. In an embodiment, controller 103also outputs a signal that represents a digital data value to be storedas a precise value and receives a signal that represents a digital datavalue that has be written and read using fulldata-correctness-guarantees in an embodiment.

In an embodiment, controller executes approximate memory operations 103a in response to processor executing application 107 and/or operatingsystem 106.

In an embodiment, controller 103 outputs and receives data asapproximate values and data as precise values in a block (or page ofdata), such as a 512-bit block. FIG. 3 illustrates digital data storedas approximate values in approximate block 300 a and digital data storedas precise values in precise block 300 b of multi-cell array 300 in MLCmemory 101.

In an embodiment, each block of memory in multi-cell array 300 includeseither precise data values (precise block 300 b) or approximate datavalues (approximate block 300 a). In alternate embodiments, a first MLCmemory array would store data as approximate values and a different MLCmemory array would store data as precise values.

In an embodiment, a predetermined number of data values (or bits) (forexample, in a “row”) are simultaneously written in parallel as precisevalues. Alternatively, a predetermined number of data values aresimultaneously written as approximate values. A row of memory cells (orother portion of MLC memory, such as bank) in a MLC memory may storeeither data values as precise values or approximate values.

In another embodiment, data values may be written into a portion of MLCmemory (such as a row) simultaneously that includes data values storedas both precise and approximate values.

Each read and write request from controller 103 to MLC memory 101specifies whether an access is approximate or precise in an embodiment.Controller 103 outputs flag information in control information of awrite or read request that identifies whether a particular memoryoperation involves approximate data or precise data in an embodiment.The use of flag information allows MLC memory 101 to avoid the overheadof storing per-block metadata.

Alternatively, operating system 106 is responsible for keeping track ofwhich memory locations or addresses in MLC memory array 300 hold data asapproximate blocks and precise blocks. In an embodiment, an allocator ofoperating system 106 keeps track of the memory locations. Application107 and/or operating system 106 may also convey the relative importanceof bits within a block, enabling more significant bits to be stored withhigher accuracy.

To specify the relative priority of bits within a block of memory, amemory operation request from controller 103 can also include a dataelement size, such as a size of data element 310 a or data element 320 aillustrated in FIG. 3. In an embodiment, a block of memory stores ahomogenous array of values of this size in each data element with thehighest-order bits being most important. For example, when application107, via operating system 107 and controller 103, stores an array ofdouble-precision floating point numbers in a block of memory,application 107 can specify a data element size of 8 bytes. MLC memory101 will prioritize the precision of each number's sign bit and exponentover its mantissa in decreasing bit order. Bit priority helps MLC memory101 and or controller 103 where to expend error protection resources tominimize the magnitude of errors when they occur.

In an embodiment, controller 103 also includes an error correctionsoftware component to correct errors. In an embodiment, one or moresoftware components and/or circuits in controller 103 may be included inMLC memory 101. Alternatively, one or more software components and/orcircuits in MLC memory 101 may be included in controller 103 inembodiments.

FIGS. 4A-4B illustrate probabilities and target ranges of analog valuesassociated with storing data as precise values and approximate values.MLC memories store an analog value, a voltage value or resistance value,and quantize the analog value to provide a digital value that representsthe measured analog value. In MLC Flash memory, the voltage value is thefloating-gate transistor's stored charge, measured via its thresholdvoltage value. In MLC PCM memory a resistance is measured by applying athreshold voltage value that injects a current into the MLC memory.

Writes and reads to an analog substrate are typically imprecise. A writeprogramming pulse, rather than adjusting the resistance or voltage by aprecise amount, changes the MLC memory randomly according to aprobability distribution, such a probability distribution 440. In anembodiment, probability distribution 440 is a normal or Gaussiandistribution of possible analog values associated with cell values 00,01, 10 and 11. In alternate embodiments, other types of probabilitydistributions may be used. During reads, material non-determinism causesthe recovered analog value to differ slightly from the analog valueoriginally stored and, over time, the stored analog value can change dueto drift. MLC memories that store data as a precise value are typicallydesigned to minimize the likelihood that write imprecision, read noise,or drift cause storage errors in the digital domain. That is, given anydigital value, a write followed by a read recovers the same digitalvalue with very high probability. So as illustrated by FIGS. 4A-B,target ranges 400-403 that are used in storing data as precise valuesare much smaller that target ranges 420-423 used to store data as anapproximate value. MLC memories that store data as approximate valueswould generally rather increase density or performance at the cost ofoccasional digital-domain storage errors.

MLC memories that store data as precise values incorporate guard bands,such as guard band 430, that account for this imprecision and attempt toprevent storage errors. These guard bands lead to tighter tolerances ontarget values, which in turn may limit write performance. Storing dataas approximate values in MLC memories reduce or eliminate guard bands toimprove write time at the cost of occasional errors.

FIG. 4B illustrates the target ranges of analog values (target range)420-423 for an MLC memory that stores data as approximate values forfour different cell values. As can be seen, target ranges 420-423 usedto store data as approximate values as compared to target ranges 400-403used to store data as precise values are substantially larger.Similarly, guard band 431 is substantially smaller than guard band 430.The target ranges for data stored as approximate values are so large, inan embodiment that a measured voltage V_(e) may correspond to either acell value 00 or 01. In comparison, guard band 430 does not allow forthis duplicity to occur when storing data as precise values.

FIG. 2 illustrates a high-level block diagram of a MLC memory 101according to an embodiment. Data, timing and/or control information istransferred to MLC memory 101 from controller 103 on signal path 104 inembodiments. Signal path 104 may include multiple signal paths to carrymultiple bits of information in parallel and/or serially. Signal path104 may also provide timing or clock information to and from MLC memory101. Timing or clock information may synchronize the reception and/ortransfer of data from and to MLC memory 101.

The control information received by MLC memory 101 may include at leastone command indicating a particular memory operation, addressinformation and flag information indicating whether associated data tobe accessed is approximate data or precise data in embodiments.

In an embodiment, the control information is provided in the form of acommand packet that includes a command value or code representing amemory operation to perform and associated address information of MLCmemory array 202. In an embodiment, a command packet also includes flaginformation that identifies whether the memory block accessed storesdata as precise or approximate values. In an embodiment, controlinformation is provided in successive fields or multi-bit positions inthe command packet. In an embodiment, at least one processor executesapplication 107 that causes a command packet to be output fromcontroller 103 to MLC memory 101. In alternate embodiments, commandpackets are not used and a bused and/or dedicated control signals areused.

Interface 200 is configured to receive and output signals representingcontrol information, data stored as approximate and/or precise values,and/or timing information on signal path 104. In an embodiment,interface 200 includes metal contact or wire. In an embodiment, signalsare transferred from interface 200 to write circuit 205 by way of signalpath 208.

In an embodiment, write circuit 205 includes write control circuit 205a, approximate write circuit 205 b, and precise write circuit 205 c. Inan embodiment, write control circuit 205 a includes registers to receivecontrol information or control signals, data and timing information inembodiments. Write control circuit 205 a (as well as read controlcircuit 206 a in embodiments) may include a phase lock loop (PLL) ordelay lock loop (DLL) to time the reception and transfer of data andcontrol information as well as time MLC memory 101 circuits. Inembodiments, write control circuit 205 a and read control circuit 206 aincludes serial-to-parallel converter circuits and/or parallel-to-serialconverter circuits in embodiments.

Approximate write circuit 205 b is responsible to store data as anapproximate value in an embodiment. Approximate write circuit 205 bstores an analog value at a particular address in MLC memory array 202by providing an amount of energy iteratively via signal path 218 toiteratively change a state of an addressed cell. In an embodiment, theamount of energy used to program an approximate value is increased inapproximate write circuit 205 b as compared to an amount of energy usedto program a cell by precise write circuit 205 c so that lessprogramming iterations are used as illustrated by FIG. 5B. In analternate embodiment, less write iterations are used because a largertarget range, such as approximate target range 420, is used asillustrated by FIG. 5C.

In particular, approximate write circuit 205 b provides a programmingpulse (P1,P2 in FIG. 5B or P1,P2,P3,P4 in FIG. 5C) and then verifies orsenses an analog value stored at a cell of MCL array 202 after eachiterative programming pulse is applied. The programming and verifying(measuring or sensing) is repeated over a plurality of iterative stepsuntil the analog value stored at the address of the MLC memory isgreater than or equal to a threshold 210, such as threshold voltage 520a. A programming pulse may have a predetermined voltage and duration.For example, programming pulse P2 has an amplitude V_(a) and duration530 as seen in FIG. 5B or a shorter duration, such as duration 510 forprogramming pulse P2.

The number of programming iterations (or pulses) used by approximatewrite circuit 205 b is less than is used in precise write circuit 205 cin embodiments as described herein. For example by comparison, FIG. 5Aillustrates providing a plurality of predetermined values in writing acell value that is stored as a precise value. In particular, a pluralityof programming pulses P1-P5, each having a particular analog amplitudeV_(a) (voltage) and duration 510 is iteratively applied and verified(measured or sensed) until the sensed cell value has an analog valuethat falls within a precise target range 500 of analog values.Distribution 501 illustrates a normal or Gaussian distribution of analogvalues corresponding to a particular digital value similar todistribution 440 shown in FIGS. 4A-B. Precise target range 500 isselected such there is high probability that the programming will resultin a data value stored correctly. In an embodiment, threshold value 500a at an end of precise target range 500 is used to compare to a sensedcell analog value and determine that the cell value has been storedcorrectly. Because precise target range 500 is smaller than approximatetarget range 520 (or not as wide) for a particular cell value, thresholdvalues associated with writing values as precise values are less thanthreshold values used to write data as an approximate value.

In an embodiment, approximate write circuit 205 b stores a block of datain MLC memory array 202, such as approximate blocks 203 a and 203 b, viasignal path 218. As described herein, approximate write circuit 205 buses at least one threshold 210, such as a threshold voltage value orthreshold resistance value, to store data as an approximate value in aMLC memory. In an embodiment, multiple thresholds (corresponding todifferent target ranges of analog values) are used for different cellvalues at different levels of a MLC memory in MLC memory array 202.

Precise write circuit 205 c is responsible to store data as precisevalues in an embodiment. Precise write circuit 205 c stores a value at aparticular address in MLC memory array 202 by providing programmingpulses iteratively via signal path 218 illustrated by FIG. 5A. Inparticular, precise write circuit 205 c provides a programming pulse andthen verifies (or senses) an analog value stored at a level of a MCLafter the programming pulse is applied. The programming and verifying isrepeated over a plurality of iterative steps until the value stored atthe address is greater than or equal to a threshold 211. MLC Flashmemory is typically written using a series of many small programmingpulses whose amplitude and duration are chosen to minimize theprobability of over-programming. A programming pulse used in precisewrite circuit 205 c may have a predetermined voltage and duration thatis less than the programming pulse used by approximate write circuit 205b.

In an embodiment, precise write circuit 205 c stores a block of data inMLC memory array 202, such as precise blocks 204 a, 204 b and 204 c. Asdescribed herein, precise write circuit 205 c uses at least onethreshold 211, such as a threshold voltage value or threshold resistancevalue, to store data as a precise value in a MLC memory of acorresponding block of data. In an embodiment, multiple thresholds(corresponding to different target ranges of analog values asillustrated in FIGS. 4A-B) are used for different cell values in MLCmemory array 202. In an embodiment, threshold value 211 is selected suchthat full data-correctness-guarantees are met in storing a value in aMLC memory.

In an embodiment, approximate write circuit 205 b and precise writecircuit 205 c may be combined.

In an embodiment, approximate write operations allow for denser cellsunder fixed energy and/or performance budgets.

In an embodiment, read circuit 206 includes read control circuit 206 a,approximate read circuit 206 b, and precise read circuit 206 c. In analternate embodiment, read circuit 206 does not include approximate readcircuit 206 b and reads data as a precise value. Approximate readcircuit 205 c is responsible to read data as an approximate value in anembodiment. Approximate read circuit 206 b reads a value at a particularaddress in MLC memory array 202 in response to control signal receivedat signal path 216 via interface 200 and outputs the data as anapproximate data to controller 103 via signal paths 216, interface 200and signal path 104.

In an embodiment, approximate read circuit 206 b reads a block of datain multi-cell array 202, such as approximate blocks 203 a and 203 b, viasignal path 214. In alternate embodiments, approximate read circuit 206b may read precise blocks as well as approximate blocks. As describedherein, approximate read circuit 205 c uses at least one threshold value212, such as a threshold voltage value or threshold resistance value, toread data as approximate data in a MLC memory. In an embodiment,multiple thresholds (corresponding to different target ranges of analogvalues) are used for different cell values at different levels of a MLCmemory in multi-cell array 202. In an embodiment, read operations aremade lower-energy by using read or pulse iterations to determine therough vicinity of a value being read, or up to approximate target range520.

In an embodiment, precise read circuit 206 c reads a block of data inMLC memory array 202, such as precise blocks 204 a, 204 b and 204 c, viasignal path 214. As described herein, precise read circuit 206 c uses atleast one threshold value 213, such as a threshold voltage value orthreshold resistance value, to read data as a precise value in a MLCmemory of a corresponding block of data. In an embodiment, multiplethresholds (corresponding to different target ranges of analog values)are used for different cell values at different levels of a MLC memoryin MLC memory array 202. In an embodiment, threshold value 213 isselected as having a higher value for a particular level (correspondingto smaller target range of analog values as illustrated in FIGS. 4A-B)than threshold value 212. In an embodiment, threshold value 212 isselected such that full data-correctness-guarantees are met in reading avalue in a MLC memory.

In an embodiment, instead of returning an exact value read, approximateread circuit 206 b returns data whose value is probabilistic following apre-profiled distribution. For example, if a value read falls in anoverlap area, such as voltage V_(e) shown in FIG. 4B, then the data maypossibly correspond to one of two values with a certain distribution.Approximate read circuit 206 b returns one or the other two valuesprobabilistically according to a relative density of each value'sprobability distribution. In an embodiment, approximate read circuit 206b includes a look-up table having corresponding probabilitydistributions for pairs of cell values that may be used to output one ofthe possible values. In an alternate embodiment, approximate readcircuit 206 b may have a software component that performs a statisticalanalysis on possible values.

FIGS. 6A-C are flow charts for writing and reading approximate values ina MLC memory in various embodiments. In embodiments, steps illustratedin FIGS. 6A-C represent the operation of hardware (e.g., processors,memories, cells, circuits), software (e.g., operating systems, softwarecomponents, applications, drivers, machine/processor executableinstructions), or a user, singly or in combinations. As one of ordinaryskill in the art would understand, embodiments may include less or moresteps shown. In various embodiments, steps illustrated may be completedsequentially, in parallel or in a different order as illustrated.

In an embodiment, a method illustrated by FIG. 6A illustrates anoperation of a MLC memory, such a MLC memory 101. Step 600 illustratesreceiving a first signal that represents a first digital value to bestored in a multi-level cell. In an embodiment, at least interface 200and/or write control circuit 205 a performs this step.

Step 601 represents receiving a first signal that indicates a firstdigital value is to be written as an approximate value. In anembodiment, at least interface 200 and/or write control circuit 205 aperforms this step.

Step 602 represents providing at least one programming pulse to themulti-level cell until a first sensed analog value from the multi-levelcell is within a first range of values. In an embodiment, approximatewrite circuit 205 b performs this step.

Step 603 represents receiving a second signal that represents a seconddigital value to be stored in a multi-level cell. In an embodiment, atleast interface 200 and/or write control circuit 205 a performs thisstep.

Step 604 represents receiving a second signal that indicates the seconddigital value is to be written as a precise value. In an embodiment, atleast interface 200 and/or write control circuit 205 a performs thisstep. Step 604 represents providing at least one programming pulse tothe multi-level cell until a second sensed analog value from themulti-level cell is within a second range of values. The first range ofvalues is wider than the second range of values. In an embodiment,precise write circuit 205 c performs this step.

In an embodiment, a method illustrated by FIG. 6B illustrates anoperation of a computing device, such a computing device 100. Step 610represents providing a signal representing a digital data value and asignal that indicates whether the digital data value is to be stored asan approximate value from a controller. In an embodiment, controller 103executing approximate memory operations 103 a performs this step.

Step 611 illustrates receiving at an interface of a multi-level cellmemory the signals. In an embodiment, MLC memory 101 performs this step,and in particular at least interface 200 and/or write control circuit205 a of MLC memory 101.

Step 612 illustrates providing a first plurality of predetermined values(such as first plurality of pulses) to a multi-level cell so a firstanalog value is stored in the multi-level cell. The first analog valueis in a first range of analog values that represents the digital valuewhen the signal indicates the data value is to be stored as anapproximate value. In an embodiment, MLC memory 101 performs this step,and in particular, at least approximate write circuit 205 b of MLCmemory 101.

Step 613 illustrates providing a second plurality of predeterminedvalues (such as a second plurality of pulses) to a multi-level cell so asecond analog value is stored in the multi-level cell. The second analogvalue is in a second range of analog values that represents the digitalvalue when the signal indicates the data value is to be stored as aprecise value. The first range of analog values is wider than the secondrange of values. In an embodiment, MLC memory 101 performs this step,and in particular, at least approximate write circuit 205 b of MLCmemory 101.

In an embodiment, a method illustrated by FIG. 6C illustrates anoperation of a controller, such controller 103 executing approximatememory operations 103 a. Step 620 represents outputting controlinformation to read a precise value at a first multi-level cell in anarray of multi-level cells. In an embodiment, controller 103 outputs thecontrol information to MLC memory 101.

Step 621 illustrates receiving a first digital value corresponding tothe precise value from a first multi-level cell. The first digital valuewas obtained by determining whether an analog value from the firstmulti-level cell was between a first range of analog values. In anembodiment, controller 103 receives the first digital value.

Step 623 illustrates outputting control information to read theapproximate value at the first multi-level cell in the array ofmulti-level cells. In an embodiment, controller 103 outputs the controlinformation to MLC memory 101.

Step 624 illustrates receiving a second digital value corresponding tothe approximate value from the first multi-level cell. The seconddigital value was obtained by determining whether an analog value fromthe second multi-level cell was between a second range of analog values.The second range of analog values is wider than the first range ofanalog values. In an embodiment, controller 103 receives the seconddigital value.

These methods may include other steps, actions and/or details that arenot discussed in these method overviews illustrated in FIGS. 6 a-C.Other steps, actions and/or details are discussed with reference toother figures and may be a part of the methods, depending on theimplementation.

In an embodiment, computing device 100 may be, but is not limited to, avideo game and/or media console. FIG. 7 will now be used to describe anexemplary video game and media console, or more generally, will be usedto describe an exemplary gaming and media system 1000 that includes agame and media console. The following discussion of FIG. 7 is intendedto provide a brief, general description of a suitable computing devicewith which concepts presented herein may be implemented. It isunderstood that the system of FIG. 7 is by way of example only. Infurther examples, embodiments describe herein may be implemented using avariety of client computing devices, either via a browser application ora software application resident on and executed by a client computingdevice. As shown in FIG. 7, a gaming and media system 1000 includes agame and media console (hereinafter “console”) 1002. In general, theconsole 1002 is one type of client computing device. The console 1002 isconfigured to accommodate one or more wireless controllers, asrepresented by controllers 1004 ₁ and 1004 ₂. The console 1002 isequipped with an internal hard disk drive and a portable media drive1006 that support various forms of portable storage media, asrepresented by an optical storage disc 1008. Examples of suitableportable storage media include DVD, CD-ROM, game discs, and so forth.The console 1002 also includes two memory unit card receptacles 1025 ₁and 1025 ₂, for receiving removable flash-type memory units 1040. Acommand button 1035 on the console 1002 enables and disables wirelessperipheral support.

As depicted in FIG. 7, the console 1002 also includes an optical port1030 for communicating wirelessly with one or more devices and two USBports 1010 ₁ and 1010 ₂ to support a wired connection for additionalcontrollers, or other peripherals. In some implementations, the numberand arrangement of additional ports may be modified. A power button 1012and an eject button 1014 are also positioned on the front face of theconsole 1002. The power button 1012 is selected to apply power to thegame console, and can also provide access to other features andcontrols, and the eject button 1014 alternately opens and closes thetray of a portable media drive 1006 to enable insertion and extractionof an optical storage disc 1008.

The console 1002 connects to a television or other display (such asdisplay 1050) via A/V interfacing cables 1020. In one implementation,the console 1002 is equipped with a dedicated A/V port configured forcontent-secured digital communication using A/V cables 1020 (e.g., A/Vcables suitable for coupling to a High Definition Multimedia Interface“HDMI” port on a high definition display 1050 or other display device).A power cable 1022 provides power to the game console. The console 1002may be further configured with broadband capabilities, as represented bya cable or modem connector 1024 to facilitate access to a network, suchas the Internet. The broadband capabilities can also be providedwirelessly, through a broadband network such as a wireless fidelity(Wi-Fi) network.

Each controller 1004 is coupled to the console 1002 via a wired orwireless interface. In the illustrated implementation, the controllers1004 are USB-compatible and are coupled to the console 1002 via awireless or USB port 1010. The console 1002 may be equipped with any ofa wide variety of user interaction mechanisms. In an example illustratedin FIG. 7, each controller 1004 is equipped with two thumb sticks 1032 ₁and 1032 ₂, a D-pad 1034, buttons 1036, and two triggers 1038. Thesecontrollers are merely representative, and other known gamingcontrollers may be substituted for, or added to, those shown in FIG. 7.

In an embodiment, a user may enter input to console 1002 by way ofgesture, touch or voice. In an embodiment, optical I/O interface 1135receives and translates gestures of a user. In another embodiment,console 1002 includes a natural user interface (NUI) to receive andtranslate voice and gesture inputs from a user. In an alternateembodiment, front panel subassembly 1142 includes a touch surface and amicrophone for receiving and translating a touch or voice, such as avoice command, of a user.

In one implementation, a memory unit (MU) 1040 may also be inserted intothe controller 1004 to provide additional and portable storage. PortableMUs enable users to store game parameters for use when playing on otherconsoles. In this implementation, each controller is configured toaccommodate two MUs 1040, although more or less than two MUs may also beemployed.

The gaming and media system 1000 is generally configured for playinggames (such as video games) stored on a memory medium, as well as fordownloading and playing games, and reproducing pre-recorded music andvideos, from both electronic and hard media sources. With the differentstorage offerings, titles can be played from the hard disk drive, froman optical storage disc (e.g., 1008), from an online source, or from MU1040. Samples of the types of media that gaming and media system 1000 iscapable of playing include:

Game titles played from CD and DVD discs, from the hard disk drive, orfrom an online streaming media source.

Digital music played from a CD in portable media drive 1006, from a fileon the hard disk drive (e.g., music in a media format), or from onlinestreaming media sources.

Digital audio/video played from a DVD disc in portable media drive 1006,from a file on the hard disk drive (e.g., Active Streaming Format), orfrom online streaming sources.

During operation, the console 1002 is configured to receive input fromcontrollers 1004 and display information on the display 1050. Forexample, the console 1002 can display a user interface on the display1050 to allow a user to select a game using the controller 1004 anddisplay state solvability information as discussed below.

FIG. 8 is a functional block diagram of the gaming and media system 1000and shows functional components of the gaming and media system 1000 inmore detail. The console 1002 has a CPU 1100, and a memory controller1102 that facilitates processor access to various types of memory,including a flash ROM 1104, a RAM 1106, a hard disk drive 1108, and theportable media drive 1006. In one implementation, the CPU 1100 includesa level 1 cache 1110 and a level 2 cache 1112, to temporarily store dataand hence reduce the number of memory access cycles made to the harddrive 1108, thereby improving processing speed and throughput.

The CPU 1100, the memory controller 1102, and various memory devices areinterconnected via one or more buses. The details of the bus that isused in this implementation are not particularly relevant tounderstanding the subject matter of interest being discussed herein.However, it will be understood that such a bus might include one or moreof serial and parallel buses, a memory bus, a peripheral bus, and aprocessor or local bus, using any of a variety of bus architectures. Byway of example, such architectures can include an Industry StandardArchitecture (ISA) bus, a Micro Channel Architecture (MCA) bus, anEnhanced ISA (EISA) bus, a Video Electronics Standards Association(VESA) local bus, and a Peripheral Component Interconnects (PCI) busalso known as a Mezzanine bus.

In one implementation, the CPU 1100, the memory controller 1102, the ROM1104, and the RAM 1106 are integrated onto a common module 1114. In thisimplementation, the ROM 1104 is configured as a flash ROM that isconnected to the memory controller 1102 via a PCI bus and a ROM bus(neither of which are shown). The RAM 1106 is configured as multipleDouble Data Rate Synchronous Dynamic RAM (DDR SDRAM) modules that areindependently controlled by the memory controller 1102 via separatebuses. The hard disk drive 1108 and the portable media drive 1006 areshown connected to the memory controller 1102 via the PCI bus and an ATAttachment (ATA) bus 1116. However, in other implementations, dedicateddata bus structures of different types can also be applied in thealternative.

In an embodiment, RAM 1106 may represent one or more processor readablememories. In an embodiment, RAM 1106 may be a Wide I/O DRAM.Alternatively, memory 402 may be Low Power Double Data Rate 3 dynamicrandom access memory (LPDDR3 DRAM) memory (also known as Low Power DDR,mobile DDR (MDDR) or mDDR). In an embodiment, memory 402 may be acombination of different types of memory.

In embodiments, RAM 1106 includes one or more arrays of memory cells inan IC disposed on a semiconductor substrate. In an embodiment, RAM 1106is included in an integrated monolithic circuit housed in a separatelypackaged device than CPU 1100.

RAM 1106 may be replaced with other types of volatile memory thatinclude at least dynamic random access memory (DRAM), molecularcharge-based (ZettaCore) DRAM, floating-body DRAM and static randomaccess memory (“SRAM”). Particular types of DRAM include double datarate SDRAM (“DDR”), or later generation SDRAM (e.g., “DDRn”).

ROM 1104 may likewise be replaced with other types of non-volatilememory including at least types of electrically erasable programread-only memory (“EEPROM”), FLASH (including NAND and NOR FLASH), ONOFLASH, magneto resistive or magnetic RAM (“MRAM”), ferroelectric RAM(“FRAM”), holographic media, Ovonic/phase change, Nano crystals,Nanotube RAM (NRAM-Nantero), MEMS scanning probe systems, MEMScantilever switch, polymer, molecular, nano-floating gate and singleelectron.

In an embodiment, ROM 1104 and RAM 1106 are replaced by MLC memory 101storing application 107 and operating system 106. Similarly, memorycontroller 1102 and CPU 1100 are replaced by controller 103 andprocessor 102 as illustrated in FIG. 1.

A three-dimensional graphics processing unit 1120 and a video encoder1122 form a video processing pipeline for high speed and high resolution(e.g., High Definition) graphics processing. Data are carried from thegraphics processing unit 1120 to the video encoder 1122 via a digitalvideo bus. An audio processing unit 1124 and an audio codec(coder/decoder) 1126 form a corresponding audio processing pipeline formulti-channel audio processing of various digital audio formats. Audiodata are carried between the audio processing unit 1124 and the audiocodec 1126 via a communication link. The video and audio processingpipelines output data to an A/V (audio/video) port 1128 for transmissionto a television or other display. In the illustrated implementation, thevideo and audio processing components 1120-1128 are mounted on themodule 1114.

FIG. 8 shows the module 1114 including a USB host controller 1130 and anetwork interface 1132. The USB host controller 1130 is shown incommunication with the CPU 1100 and the memory controller 1102 via a bus(e.g., PCI bus) and serves as host for the peripheral controllers 1004₁-1004 ₄. The network interface 1132 provides access to a network (e.g.,Internet, home network, etc.) and may be any of a wide variety ofvarious wire or wireless interface components including an Ethernetcard, a modem, a wireless access card, a Bluetooth module, a cablemodem, and the like.

In the implementation depicted in FIG. 8, the console 1002 includes acontroller support subassembly 1140 for supporting the four controllers1004 ₁-1004 ₄. The controller support subassembly 1140 includes anyhardware and software components to support wired and wireless operationwith an external control device, such as for example, a media and gamecontroller. A front panel I/O subassembly 1142 supports the multiplefunctionalities of power button 1012, the eject button 1014, as well asany LEDs (light emitting diodes) or other indicators exposed on theouter surface of console 1002. Subassemblies 1140 and 1142 are incommunication with the module 1114 via one or more cable assemblies1144. In other implementations, the console 1002 can include additionalcontroller subassemblies. The illustrated implementation also shows anoptical I/O interface 1135 that is configured to send and receivesignals that can be communicated to the module 1114.

The MUs 1040 ₁ and 1040 ₂ are illustrated as being connectable to MUports “A” 1030 ₁ and “B” 1030 ₂ respectively. Additional MUs (e.g., MUs1040 ₃-1040 ₆) are illustrated as being connectable to the controllers1004 ₁ and 1004 ₃, i.e., two MUs for each controller. The controllers1004 ₂ and 1004 ₄ can also be configured to receive MUs. Each MU 1040offers additional storage on which games, game parameters, and otherdata may be stored. In some implementations, the other data can includeany of a digital game component, an executable gaming application, aninstruction set for expanding a gaming application, and a media file.When inserted into the console 1002 or a controller, the memorycontroller 1102 can access the MU 1040.

A system power supply module 1150 provides power to the components ofthe gaming system 1000. A fan 1152 cools the circuitry within theconsole 1002.

An application 1160 comprising processor readable instructions is storedon the hard disk drive 1108. When the console 1002 is powered on,various portions of the application 1160 are loaded into RAM 1106,and/or caches 1110 and 1112, for execution on the CPU 1100, wherein theapplication 1160 is one such example. Various applications can be storedon the hard disk drive 1108 for execution on CPU 1100.

The console 1002 is also shown as including a communication subsystem1170 configured to communicatively couple the console 1002 with one ormore other computing devices (e.g., other consoles). The communicationsubsystem 1170 may include wired and/or wireless communication devicescompatible with one or more different communication protocols. Asnon-limiting examples, the communication subsystem 1170 may beconfigured for communication via a wireless telephone network, or awired or wireless local- or wide-area network. In some embodiments, thecommunication subsystem 1170 may allow the console 1002 to send and/orreceive messages to and/or from other devices via a network such as theInternet. In specific embodiments, the communication subsystem 1170 canbe used to communicate with a coordinator and/or other computingdevices, for sending download requests, and for effecting downloadingand uploading of digital content. More generally, the communicationsubsystem 1170 can enable the console 1002 to participate onpeer-to-peer communications.

The gaming and media system 1000 may be operated as a standalone systemby simply connecting the system to display 1050 (FIG. 7), a television,a video projector, or other display device. In this standalone mode, thegaming and media system 1000 enables one or more players to play games,or enjoy digital media, e.g., by watching movies, or listening to music.However, with the integration of broadband connectivity made availablethrough network interface 1132, or more generally the communicationsubsystem 1170, the gaming and media system 1000 may further be operatedas a participant in a larger network gaming community, such as apeer-to-peer network.

The above described console 1002 is just one example of the computingdevice 100 discussed above with reference to FIG. 1 and various otherFigures. As was explained above, there are various other types ofcomputing devices with which embodiments described herein can be used.

FIG. 9 is a block diagram of one embodiment of a computing device 100which may host at least some of the software components illustrated inFIG. 1. In its most basic configuration, computing device 1800 typicallyincludes one or more processing units 1802 including one or more CPUsand one or more GPUs. Depending on the exact configuration and type ofcomputing device, system memory 1804 may include volatile memory 1805(such as RAM), non-volatile memory 1807 (such as ROM, flash memory,etc.) or some combination of the two. Computing device 1800 alsoincludes system memory 1804 that may be replaced by MLC memory 101 asillustrated in FIG. 1. This most basic configuration is illustrated inFIG. 9 by dashed line 1806. Additionally, device 1800 may also haveadditional features/functionality. For example, device 1800 may alsoinclude additional storage (removable and/or non-removable) including,but not limited to, magnetic or optical discs or tape. Such additionalstorage is illustrated in FIG. 9 by removable storage 1808 andnon-removable storage 1810.

Device 1800 may also contain communications connection(s) 1812 such asone or more network interfaces and transceivers that allow the device tocommunicate with other devices. Device 1800 may also have inputdevice(s) 1814 such as keyboard, mouse, pen, voice input device, touchinput device, gesture input device, etc. Output device(s) 1816 such as adisplay, speakers, printer, etc. may also be included. These devices arewell known in the art so they are not discussed at length here.

In an embodiment, device 1800 is a cellular telephone that executes anapplication 107, such as an application that analyzes and/or receivessensor data, including for example, global positioning system (GPS)sensor data and/or accelerometer data from sensors positioned on thecellular telephone. In an embodiment, such sensor data may be stored asapproximate data.

The foregoing detailed description of the inventive system has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the inventive system to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. The described embodiments were chosen inorder to best explain the principles of the inventive system and itspractical application to thereby enable others skilled in the art tobest utilize the inventive system in various embodiments and withvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the inventive system be defined by theclaims appended hereto.

What is claimed is:
 1. A device, comprising: a controller for providinga digital data value; and a multi-level cell memory including an arrayof multi-level cells, each multi-level cell in the array beingconfigured to utilize a respective probability distribution of likelyanalog values to represent a stored digital data value, and one or morewrite circuits configured for storing the digital data value as anapproximate analog value by writing to a multi-level cell in the arrayusing analog values within a target range that overlaps the probabilitydistributions associated with digital data values stored in adjacentmulti-level cells in the array.
 2. The device of claim 1 in which eachmulti-level cell in the array is adapted for storing at least twodigital data values.
 3. The device of claim 1 in which each multi-levelcell in the array is selected from one of a multi-level flash memory ora multi-level phase change memory.
 4. The device of claim 1 in which thecontroller further sets a flag that indicates when the digital datavalue is to be stored as a precise analog value and when the digitaldata value is to be stored as an approximate analog value.
 5. The deviceof claim 4 in which the one or more write circuits are furtherconfigured to store the digital data value as a precise analog valueresponsively to the flag by writing to a multi-level cell using analogvalues within a second target range that does not overlap theprobability distributions associated with digital data values stored inadjacent multi-level cells in the array.
 6. The device of claim 5 inwhich the target range of analog values is narrower than the secondtarget range of analog values and, when the digital data value is storedas a precise analog value, the multi-level cell memory incorporatesguard bands.
 7. The device of claim 6 in which the target range ofanalog values includes a first plurality of programming pulses having afirst voltage value, the second target range of analog values includes asecond plurality of programming voltages having a second voltage value,and the first voltage value is greater than the second voltage value. 8.The device of claim 6 in which the target range of analog valuesincludes a first plurality of programming pulses having a firstduration, the second target range of analog values includes a secondplurality of programming voltages having a second duration, and thefirst duration is greater than the second duration.
 9. The device ofclaim 1 in which the one or more write circuits is further configured toprovide at least one programming pulse to the multi-level cell until asensed analog value from the multi-level cell is within the target rangeof analog values or the sensed analog value is within the second targetrange of analog values.
 10. The device of claim 9 in which the sensedanalog value is one of a voltage value or a resistance value.
 11. Amethod for reading a digital data value as an approximate value from anarray of multi-level cells, the method comprising: receiving controlinformation at a read control circuit to read the digital data value atan address in the array; performing a read operation on a block of dataat the address in array to obtain an analog value representing one oftwo possible digital data values, each of the two possible digital datavalues being represented by analog values falling within an associatedpre-profiled probability distribution; selecting one of the two possibledigital data values based on a density of each digital data value'sprobability distribution; and returning the selected digital data valueto the read control circuit responsively to the received controlinformation.
 12. The method of claim 11 further including performing alook up of the pre-profiled probability distributions associated withthe two possible digital data values in a look up table.
 13. The methodof claim 11 further including performing a statistical analysis on thetwo possible digital data values when performing the selecting.
 14. Themethod of claim 11 further including receiving control information toread a digital data value as a precise value at an address in the arrayof multi-level cells, performing a read operation on a block of data atthe address in the multi-level cell array to obtain an analog value, anddetermining if the analog value exceeds a threshold at which a fulldata-correctness-guarantee is obtained.
 15. A multi-level cell memoryarranged for storing a digital data value as an approximate value havingrelaxed precision, comprising: an interface to a controller; a pluralityof multi-level cells configured as an array; and a write control circuitadapted for receiving, from the controller over the interface, a digitaldata value to be stored in a portion of the array; receiving, from thecontroller over the interface, an indication that the digital data valueis to be written as the approximate value; responsively to theindication, writing the digital data value as an approximate value byiteratively providing one or more programming pulses to the multi-levelcell array until a sensed analog value falls within a first target rangeof analog values, the first target range of analog values being widerthan a second target range of analog values utilized when the digitaldata value is written as a precise value with full data-correctness. 16.The multi-level cell memory of claim 15 further comprising a readcontrol circuit adapted for determining if an analog value read from amulti-level cell falls within the first target range or second targetrange and for returning an approximate value when the read analog valuefalls within the first target range and returning a precise value whenthe read analog values falls within the second target range.
 17. Themulti-level cell memory of claim 16 in which the write control circuitis adapted for writing both an approximate value and a precise valueinto a single multi-level cell in the array.
 18. The multi-level cellmemory of claim 16 in which the write control circuit is adapted forproviding programming pulses with greater amounts of energy when writingapproximate values than when writing precise values.
 19. The multi-levelcell memory of claim 15 in which the write control circuit is furtheradapted for writing the digital data value as a precise value with fulldata-correctness by iteratively providing one or more programming pulsesto the multi-level cell array until a sensed analog value falls withinthe second target range of analog values, the programming pulses forwriting a precise value being shorter in duration, or having a lessermagnitude, or using more iterations than the programming pulses forwriting an approximate value.
 20. The multi-level cell memory of claim15 in which the write control circuit comprises one of phased lock loopor delay lock loop adapted for performing timing of data and controlinformation transfer and reception over the interface.